Tube and fin type heat exchangers employing hairpin tubes (U tubes) or straight tubes are assembled into a mechanical tube expander by expanding the tubes into interference fit with the fins and end sheets of the heat exchanger. The hairpin tubes (U tubes) are comprised of two straight legs and a bend which is bent through an arc of 180.degree.. The length of the two straight legs usually determines the number of fins that are to be stacked one on top of the other and laced through holes provided in the fins.
One of the problems associated with a taking of an assembly of fins loosely stacked on the straight leg portions of the hairpin tubes and effecting a fixing of each of the fins to the hairpin tubes has been controlling the position at which each of the fins individually becomes affixed to the straight leg portion of the hairpin tubes. If one of the fins becomes affixed to the tube prematurely or not soon enough, a gap will form between mutually adjacent fins or mutually adjacent fins will be pushed into tighter relationship with one another and appear to be crushed (or may even be crushed) when viewed from the side edges of the fins. Further, the amount of stick out of the distal end of the straight leg portions of the hairpin tubes beyond the endmost fin remote from the 180.degree. bend is oftentimes uneven due to the crushing of the fin pack and not satisfactory to the customer purchasing the assembled coil. In addition, the length of the straight leg portions are known to shrink as the straight leg portions are expanded. This known shrinkage factor is further complicated by a growth in the height of the fin pack or coil height dimension as the tubes are expanded. These complicated relationships have resulted in undesired crushing of the fin pack, especially when the consistency in the material of the tubes varies. Thus, an apparatus which will effect an assembly of fins onto the straight leg portions of hairpin tubes and avoid the disadvantages mentioned above is deemed desirable.
Accordingly, it is an object of this invention to provide a mechanical tube expander having separate drive means for effecting a selective and coordinated movement of each of the pressure plate, the stripper plate and a support structure for an endmost fin in an assembly of fins relative to each other and in response to a movement of the expander rods and the tube expanding structure thereon into the straight leg portions of the tubes which effects an enlarging of the diameter of the straight leg portions to effect a fixing of each of the fins to the hairpin tubes.
It is a further object of this invention to provide a mechanical tube expander, as aforesaid, which has a control panel having controls thereon enabling the operator to set up the machine for differing coil heights while remaining at the control panel.
It is a further object of this invention to provide a mechanical tube expander, as aforesaid, wherein structure is provided for compensating for the shrinkage of the length of the straight leg portions and the simultaneous growth in the height dimension of the fin pack or coil height.
It is a further object of this invention to provide a mechanical tube expander, as aforesaid, wherein the separate drive means for effecting a selective and coordinated movement of each of the pressure plate, the stripper plate and the support for an endmost fin or end sheet is precisely controlled by a preprogrammed control circuit precisely moving each of the aforesaid pressure plate, stripper plate and support structure at precisely the correct rate of speed and at the correct moment in time to bring about the desired assembly of fins.
It is a further object of this invention to provide a mechanical tube expander, as aforesaid, which is easy to operate and permits simple compensation for minor part variations.